Heater problem at idle?
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This is a discussion on Heater problem at idle? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I've searched for answers here and at NASIOC (which appears to be down at the moment) on this issue. The ...

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    Heater problem at idle?

    I've searched for answers here and at NASIOC (which appears to be down at the moment) on this issue. The short version is that I can't get any heat from my car with a fully warmed engine while at idle. Any other RPM level produces correspondingly hotter temps from the heater. My first guess is thermostat but the car has only 65K miles. Also, wouldn't the symptoms indicate the thermostat is staying open? When they fail don't they normally fail in the closed position. The car exhibits no overheating symptoms. Thanks for any help you can provide.

    Scott
    '02 WRX

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    Registered User tarbaj's Avatar
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    The thermostat effects the coolant mix flowing through the radiator. The heater core would not be effected by it failing. Your heater core may be going bad but that seems pretty premature on an 02 with only 65K. The heater core on my 91 Maxima was going it exhibited the same thing. At idle it blew cold air but driving it was warm as could be. It had 140K on it though.

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    Well, you were right on target. It's the heater core. And yes, it's a very premature problem for a car with 65K miles. A shop measured my heater core inlet and outlet temps yesterday... 140 degrees in, 80 degrees out. I was told that 30 degrees is about the max difference for normal operation. Let's hope a backflush clears up the problem. I hear a heater core replacement is no small task. Good thing I have an extended warranty.

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    I currently have the same problem. I wonder what it cost to get a replacement.

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    .... and I'm only at 37,000 miles.

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    He simply abides. SD_GR's Avatar
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    Did either of you just flush your coolant?
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    Quote Originally Posted by SD_GR
    Did either of you just flush your coolant?
    I removed by turbo during the summer and had some coolant spills. After installing the turbo (same stock turbo) I went back and topped off the coolant. Could that affected heating during idle?

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    He simply abides. SD_GR's Avatar
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    If it were recent, you might have still had some air bubbles in the system and the heater core would not be receiving good flow. Slim chance, more of a wild guess.

    Is the car's coolant temperature, as you see it on the gauge in the dash, up to normal, higher, or lower than normal? Can you eyeball the hoses to the heater core from the engine bay and see they're OK?
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    A coolant flush fixed my problem. $130 at the dealer. An independent shop wanted more.

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    Registered User Darrell's Avatar
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    Quote Originally Posted by e28fixer
    Also, wouldn't the symptoms indicate the thermostat is staying open? When they fail don't they normally fail in the closed position?
    No, thermostats are designed to fail in the open position to prevent engine overheating.


    Quote Originally Posted by tarbaj
    The thermostat effects the coolant mix flowing through the radiator. The heater core would not be effected by it failing.
    The heater core temperature would certainly be affected by a failed (open) thermostat, because coolant would always be flowing to the radiator, thus lowering the temperature of the coolant throughout the cooling system.

    Back to the original problem, at idle, the water pump isn't turning as fast as it turns are higher rpms, so you aren't moving the warm coolant to the heater core as quickly while at idle. This was a problem that I experienced in my 91 Mazda Protege. The heat was much better after I changed the thermostat and flushed the cooling system. You may also have debris (leaves and such) built up on the heater core that is preventing proper air flow through the heater core.
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    I have the factory service manual on CD for 2002 WRX and will check it tonight for visuals. I want to see the schematics of the unit just to get a feel for what it looks like and if I will be able to do anything to solve the problem. The coolant flush shouldn't be too much of an issue. It's been below 20F and I ain't going to do anything unless I have to. Thanks all for the input.

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    Quote Originally Posted by Darrell
    No, thermostats are designed to fail in the open position to prevent engine overheating.
    Actually only the fail safe thermostats are designed to fail open. Most will fail closed.

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    I guess I have only had to deal with fail-safe thermostats then because I've never seen a modern thermostat fail closed, but that doesn't mean it can't happen!
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    Quote Originally Posted by Darrell
    I guess I have only had to deal with fail-safe thermostats then because I've never seen a modern thermostat fail closed, but that doesn't mean it can't happen!
    happened to my pontiac twice and they were new thermostats and ive seen many other cars do it and crack heads from heat and all.

    btw my cars doing the same crap at idle too. i put in 1 gallon of anti. and about 4/5ths of water for the radiator and since then its been doing it too.

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    Registered User hekeener's Avatar
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    same thing...

    Just wanted to add my 2 cents... I had the same problem and simply draining and re-filling the coolant following the maintenance service manual fixed it. Guess I was pretty low on coolant...
    Blubaru - WRB Wagon

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